//: concurrency/CountDownLatchDemo.java
package concurrency;

import java.util.concurrent.*;
import java.util.*;

import static net.mindview.util.Print.*;

// Performs some portion of a task:
class TaskPortion implements Runnable
{
    private static int counter = 0;
    
    private final int id = counter++;
    
    private static Random rand = new Random(47);
    
    private final CountDownLatch latch;
    
    TaskPortion(CountDownLatch latch)
    {
        this.latch = latch;
    }
    
    public void run()
    {
        try
        {
            doWork();
            latch.countDown();
        }
        catch (InterruptedException ex)
        {
            // Acceptable way to exit
        }
    }
    
    public void doWork()
        throws InterruptedException
    {
        TimeUnit.MILLISECONDS.sleep(rand.nextInt(2000));
        print(this + "completed");
    }
    
    public String toString()
    {
        return String.format("%1$-3d ", id);
    }
}

// Waits on the CountDownLatch:
class WaitingTask implements Runnable
{
    private static int counter = 0;
    
    private final int id = counter++;
    
    private final CountDownLatch latch;
    
    WaitingTask(CountDownLatch latch)
    {
        this.latch = latch;
    }
    
    public void run()
    {
        try
        {
            latch.await();
            print("Latch barrier passed for " + this);
        }
        catch (InterruptedException ex)
        {
            print(this + " interrupted");
        }
    }
    
    public String toString()
    {
        return String.format("WaitingTask %1$-3d ", id);
    }
}

public class CountDownLatchDemo
{
    static final int SIZE = 100;
    
    public static void main(String[] args)
        throws Exception
    {
        ExecutorService exec = Executors.newCachedThreadPool();
        // All must share a single CountDownLatch object:
        CountDownLatch latch = new CountDownLatch(SIZE);
        for (int i = 0; i < 10; i++)
            exec.execute(new WaitingTask(latch));
        for (int i = 0; i < SIZE; i++)
            exec.execute(new TaskPortion(latch));
        print("Launched all tasks");
        exec.shutdown(); // Quit when all tasks complete
    }
} /* (Execute to see output) */// :~
